Vehicular ad hoc networks (VANETs) leverage the communication system of Intelligent Transportation Systems (ITS). Recently, Delay-Tolerant Network (DTN) routing protocols have increased their popularity among the research community for being used in non-safety VANET applications and services like traffic reporting. Vehicular DTN protocols use geographical and local information to make forwarding decisions. However, current proposals only consider the selection of the best candidate based on a local-search. In this paper, we propose a generic Geographical Heuristic Routing (GHR) protocol that can be applied to any DTN geographical routing protocol that makes forwarding decisions hop by hop. GHR includes in its operation adaptations simulated annealing and Tabu-search meta-heuristics, which have largely been used to improve local-search results in discrete optimization. We include a complete performance evaluation of GHR in a multi-hop VANET simulation scenario for a reporting service. Our study analyzes all of the meaningful configurations of GHR and offers a statistical analysis of our findings by means of MANOVA tests. Our results indicate that the use of a Tabu list contributes to improving the packet delivery ratio by around 5% to 10%. Moreover, if Tabu is used, then the simulated annealing routing strategy gets a better performance than the selection of the best node used with carry and forwarding (default operation).

Ad hoc networks have attracted much attention from the research community over the last years and important technical advances have risen as a consequence. These networks are foreseen as an important kind of next generation access networks, where multimedia services will be demanded by end users from their wireless devices everywhere. In this thesis, we specially focus our research work on mobile ad hoc networks (MANETs) and on vehicular ad hoc networks (VANETs), two kind of ad hoc networks over which interesting multimedia services can be provided. The special haracteristics of MANETs/VANETs, such as mobility, dynamic network topology (specially in VANETs), energy constraints (in case of MANETs), infrastructureless and variable link capacity, make the QoS (Quality of Service) provision over these networks an important challenge for the research community. Due to that, there is a need to develop new routing protocols specially designed for MANETs and VANETs able to provide multimedia services.
The main objective of this thesis is to contribute in the development of the communication framework for MANETs and VANETs to improve decisions to select paths or next hops in the moment of forwarding video-reporting messages. In this way, it would be possible to have a quick answer to manage daily problems in the city and help the emergency units (e.g., police, ambulances, health care units) in case of incidents (e.g., traffic accidents). Furthermore, in case of VANETs, a real scenario must be created and thus we have analysed the presence of obstacles in real maps. Also, in case of an obstacle found between the current forwarding node and the candidate next forwarding node, the packet is stored in a buffer, for a maximum time, until a forwarding neighbour node is found; otherwise, the packet is dropped. To improve the communication framework for MANETs, we propose a new routing protocol based on a game-theoretical scheme for N users specially designed to transmit video-reporting messages. Our proposal makes the network more efficient and provides a higher degree of satisfaction of the users by receiving much more packets with a lower average end-to-end delay, lower jitter and higher PSNR (Peak Signal-to-Noise Ratio).
In addition, we propose a geographical routing protocol for VANETs that considers multiple metrics named 3MRP (Multimedia Multimetric Map-Aware Routing Protocol) [1]. 3MRP is a geographical protocol based on hop-by-hop forwarding. The metrics considered in 3MRP are the distance, the density of vehicles in transmission range, the available bandwidth, the future trajectory of the neighbouring nodes and the MAC layer losses. Those metrics are weighted to obtain a multimetric score. Thus, a node selects another node among its neighbours as the best forwarding node to increase the percentage of successful packet delivery, minimizing the average packet delay and offering a certain level of quality and service. Furthermore, a new algorithm named DSW (Dynamic Self-configured Weights) computes for each metric its corresponding weight depending on the current network conditions. As a consequence, nodes are classiffied in a better way.

One of the main concerns of the cities' administration is mobility management. In Intelligent Transportation Systems (ITS), pedestrians, vehicles and public transportation systems could share information and react to any situation in the city. The information sensed by vehicles could be useful for other vehicles and for the mobility authorities. Vehicular Ad hoc Networks (VANETs) make possible the communication between vehicles (V2I) and also between vehicles and fixed infrastructure (V2I) managed by the city's authorities. In addition, VANET routing protocols minimize the use of fixed infrastructure since they employ multi-hop V2V communication to reach reporting access points of the city.
This thesis aims to contribute in the design of VANET routing protocols to enable reporting services (e.g., vehicular traffic notifications) in urban environments. The first step to achieve this global objective has been the study of components and tools to mimic a realistic VANET scenario. Moreover, we have analyzed the impact of the realism of each one of those components in the simulation results.
Then, we have improved the Address Resolution procedure in VANETs by including it in the routing signaling messages. Our approach simplifies the VANET operation and increases the packet delivery ratio as consequence. Afterwards, we have tackled the issue of having duplicate packets in unicast communications and we have proposed routing filters to lower their presence. This way we have been able to increase the available bandwidth and reduce the average packet delay with a slight increase of the packet losses.
Besides, we have proposed a Multi-Metric Map aware routing protocol (MMMR) that incorporates four routing metrics (distance, trajectory, vehicle density and available bandwidth) to take the forwarding decisions. With the aim of increasing the number of delivered packets in MMMR, we have developed a Geographical Heuristic Routing (GHR) algorithm. GHR integrates Tabu and Simulated Annealing heuristic optimization techniques to adapt its behavior to the specific scenario characteristics. GHR is generic because it could use any geographical routing protocol to take the forwarding decisions. Additionally, we have designed an easy to implement forwarding strategy based on an extended topology information area of two hops, called 2-hops Geographical Anycast Routing (2hGAR) protocol. Results show that controlled randomness introduced by GHR improves the default operation of MMMR. On the other hand, 2hGAR presents lower delays than GHR and higher packet delivery ratio, especially in high density scenarios.
Finally, we have proposed two mixed (integer and linear) optimization models to detect the best positions in the city to locate the Road Side Units (RSUs) which are in charge of gathering all the reporting information generated by vehicles.

Road safety applications envisaged for VANETs depend largely on the exchange of messages to deliver information to the concerned vehicles. In the last years, several dissemination protocols have been presented in the literature. In this paper we study and evaluate the dissemination of emergency messages in realistic vehicular scenarios. In the evaluation, some protocols are examined from two perspectives: qualitative and quantitative. We identify the principal mechanisms of dissemination and examine the factors that most impact on the simulation results. In addition, we investigate the effects of the shadows of buildings and other vehicles in the performance of the dissemination protocols. The simulation results suggest the need to include scenarios with fixed and mobile obstacles to increase the credibility of the performance of the evaluated protocols.

Mobile ad hoc networks (MANETs) are infrastructureless networks formed by wireless mobile devices. Routing in MANETs is a process where the best path will be selected so that packets will be forwarded. When a MANET is heavily loaded, single path routing begins to have congestion problems. To cope with this issue, multipath routing protocols were proposed improving the single path routing in terms of packet delivery ratio and quality of service (QoS). Normally, QoS metrics are used to classify paths in order to chose those (i.e., number of paths >2) who satisfy the QoS-user-requirements. Besides, paths are classified with an equal metrics weights which we do not consider as an optimal way. In this article, we aimed to design a new form of distributing weight values for metrics so that paths would be classified in a better way. Each time we want to classify paths, our proposal seeks to give a proper value to each metric weight depending on the metric current value with respect to an average one previously defined. We consider that depending on the variation of metric value, a corresponding weight to this current variation must be given. To achieve that, a simple algorithm has been designed. Finally, paths are classified taking into account our algorithm to calculate all weights value. Simulations have been done to show the benefits of our proposal where interfering traffic and mobility of the nodes are present.

MobilitApp is a platform designed to provide smart mobility services in urban areas. It is designed to help citizens and transport authorities alike. Citizens will be able to access the MobilitApp mobile application and decide their optimal transportation strategy by visualising their usual routes, their carbon footprint, receiving tips, analytics and general mobility information, such as traffic and incident alerts. Transport authorities and service providers will be able to access information about the mobility pattern of citizens to offer their best services, improve costs and planning. The MobilitApp client runs on Android devices and records synchronously, while running in the background, periodic location updates from its users. The information obtained is processed and analysed to understand the mobility patterns of our users in the city of Barcelona, Spain.

In this paper, we propose a simple and scalable optimization model for the deployment of road site units (RSUs). The model takes advantage of the inherent stochasticity provided by the vehicles’ movements by using mobility traces to determine which are the best positions to place RSUs to maximize connectivity in a multi-hop VANET scenario and keep the number of RSU as low as possible. Our simulations results validate that the solutions offered by our model are accurate.

The prevention of accidents is one of the most important goals of ad hoc networks in smart cities. When an accident happens, dynamic sensors (e.g., citizens with smart phones or tablets, smart vehicles and buses, etc.) could shoot a video clip of the accident and send it through the ad hoc network. With a video message, the level of seriousness of the accident could be much better evaluated by the authorities (e.g., health care units, police and ambulance drivers) rather than with just a simple text message. Besides, other citizens would be rapidly aware of the incident. In this way, smart dynamic sensors could participate in reporting a situation in the city using the ad hoc network so it would be possible to have a quick reaction warning citizens and emergency units. The deployment of an efficient routing protocol to manage video-warning messages in mobile Ad hoc Networks (MANETs) has important benefits by allowing a fast warning of the incident, which potentially can save lives. To contribute with this goal, we propose a multipath routing protocol to provide video-warning messages in MANETs using a novel game-theoretical approach. As a base for our work, we start from our previous work, where a 2-players game-theoretical routing protocol was proposed to provide video-streaming services over MANETs. In this article, we further generalize the analysis made for a general number of N players in the MANET. Simulations have been carried out to show the benefits of our proposal, taking into account the mobility of the nodes and the presence of interfering traffic.Finally, we also have tested our approach in a vehicular ad hoc network as an incipient start point to develop a novel proposal specifically designed for VANETs.

Buildings are important elements of cities for VANETs, since these obstacles
may attenuate communications between vehicles. Consequently, the impact of buildings has
to be considered as part of the attenuation model in VANET simulations of urban scenarios.
However, the more elaborated the model, the more information needs to be processed during
the simulation, which implies longer processing times. This complexity in simulations is
not always worth it, because simplified channel models occasionally offer very accurate
results. We compare three approaches to model the impact of buildings in the channel model
of simulated VANETs in two urban scenarios. The simulation results for our evaluation
scenarios of a traffic-efficiency application indicate that modeling the influence of buildings
in urban areas as the total absence of communication between vehicles gives similar results
to modeling such influence in a more realistic fashion and could be considered a conservative
bound in the performance metrics.

The interest in vehicular communications has increased notably. In this paper, the use of the address resolution (AR) procedures is studied for vehicular ad hoc networks (VANETs).We analyse the poor performance of AR transactions in such networks and we present a new proposal called coherent, automatic address resolution (CAAR). Our approach inhibits the use of AR transactions and instead increases the usefulness of routing signalling to automatically match the IP and MAC addresses. Through extensive simulations in realistic VANET scenarios using the Estinet simulator, we compare our proposal CAAR to classical AR and to another of our proposals that enhances AR for mobile wireless networks, called AR+. In addition, we present a performance evaluation of the behaviour of CAAR, AR and AR+ with unicast traffic of a reporting service for VANETs. Results show that CAAR outperforms the other two solutions in terms of packet losses and furthermore, it does not introduce additional overhead.

A primary aim of wireless ad-hoc networks is to deliver data in areas where there is no pre-defined infrastructure. In these networks, the users, but also the network entities can be potentially mobile. Wireless ad-hoc networks have recently witnessed their fastest growth period ever in history. Real wireless ad-hoc networks are now implemented, deployed and tested, and this trend is likely to increase in the future. However, as such networks are increasingly complex, performance modeling and evaluation play a crucial part in their design process to ensure their successful deployment and exploitation in practice.
This special issue on Modeling and Performance Evaluation of Wireless Ad-Hoc Networks aims to open a new critical debate on the evaluation of wireless ad-hoc networks. It includes original theoretical and/or practical contributions, from researchers and practitioners that identify and address issues in evaluating wireless ad-hoc networks.

Message encryption does not prevent eavesdroppers from unveiling who is communicating with whom, when, or how frequently, a privacy risk wireless networks are particularly vulnerable to. The Crowds protocol, a well-established anonymous communication system, capitalizes on user collaboration to enforce sender anonymity. This work formulates a mathematical model of a Crowd-like protocol for anonymous communication in a lossy network, establishes quantifiable metrics of anonymity and quality of service (QoS), and theoretically characterizes the trade-off between them. The anonymity metric chosen follows the principle of measuring privacy as an attacker's estimation error. By introducing losses, we extend the applicability of the protocol beyond its original proposal. We quantify the intuition that anonymity comes at the expense of both delay and end-to-end losses. Aside from introducing losses in our model, another main difference with respect to the traditional Crowds is the focus on networks with stringent QoS requirements, for best effort anonymity, and the consequent elimination of the initial forwarding step. Beyond the mathematical solution, we illustrate a systematic methodology in our analysis of the protocol. This methodology includes a series of formal steps, from the establishment of quantifiable metrics all the way to the theoretical study of the privacy QoS trade-off. Copyright (c) 2013 John Wiley & Sons, Ltd.

Obstacles in Vehicular ad hoc networks (VANETs) in urban scenarios are an important issue. Normally, in traffic simulators vehicles can send/receive packets between each other if they are in the same transmission range no matter if an obstacle is presented or not between them. For this reason, checking if there is an obstacle between sender and receiver is an important goal. In this paper, we present a program named REVsim1.0 (Realistic Environment for Vanets simulation) [1] capable to detect at each instant of time if between a sender and a receiver a communication can be established or conversely, if an obstacle is found and such a communication is not possible. Parameters such as a, ß, road resolution and transmission range have been defined and used in our proposed algorithm. Finally, a validation of our algorithm is shown.

Many proposals have studied the optimization of
the EDCA mechanism used by the IEEE 802.11p MAC layer to
provide QoS. In this work, we focus on the queuing process done
by the different Access Categories (ACs). We propose the use
of a single common buffer with a prioritized buffer allocation
algorithm inspired on the MAX-MIN principle for a fair sharing
of a common resource. We test the proposed algorithm with a
fixed and a dynamic guaranteed queue size for each AC. Results
obtained from simulations in a multihop VANET scenario show
that our approach outperforms traditional queuing used in MAC
802.11p.

This paper proposes a mixed linear and integer optimization model for multi-hop ad-hoc networks to select the positions of the gateways over a certain area. This model mimics the routing behavior of such network and takes into account the maximum bandwidth capacity of the network gateways. We also include a suboptimal solution for the cases in which the complexity or the amount of the data make the optimal solution infeasible. Results in a pedestrian mesh network and in a VANET scenarios show that the model locates gateways in an efficient way and that the suboptimal solution is close to the optimal one in terms of the number of required gateways or the common selected gateways.

Buffer overflow is an important phenomenon in data networks that has much bearing on the overall network performance. Such overflow critically depends on the amount of storage space allotted to the transmission channels. To properly dimension this buffering capacity a detailed knowledge of some set of probabilities is needed. In real practice, however, that information is seldom available, and only a few average values are at the analyst disposal. In this paper, the use of a solution to this quandary based on maximum entropy is proposed. On the other hand, when wireless devices are taken into account, the transmission over a shared medium imposes additional restrictions. This paper also presents an extension of the maximum entropy approach for this kind of devices. The main purpose is that wireless nodes become able to dynamically self-configure their buffer sizes to achieve more efficient memory utilization while keeping bounded the packet loss probability. Simulation results using different network settings and traffic load conditions demonstrate meaningful improvement in memory utilization efficiency. This could potentially benefit devices of different wireless network technologies like mesh routers with multiple interfaces, or memory constraint sensor nodes. Additionally, when the available memory resources are not a problem, the buffer memory reduction also contributes to prevent the high latency and network performance degradation due to overbuffering. And it also facilitates the design and manufacturing of devices with faster memory technologies and future all-optical routers.

In this paper, we review the workflow of the channel and physical layer modules in VANET simulations and briefly survey some of the most used propagation and packet error models in network simulators for this kind of networks. Through numerical simulations, we compare these propagation models working with a realistic and straightforward packet error model. Our results indicate that there is not a most conservative propagation model and that conservative models vary with the channel capacity. Furthermore, different propagation models specifically designed for VANETs obtain very close results in channels with intermediate capacities.

Objectives and problems to be solved:%LThis project aims to develop a MF-SOFC stack with a nominal rating of ~20 kWe, which will be suitable for retrofitting with internal reforming modules aggregating ~50 kWe. Design and manufacturing specifications will be produced, including procedures of building and operating a sub-megawatt system. The universal MF-SOFC module, which is the building block of the system, requires scale up in rating and performance in line with commercial targets of durability, reliability and cost. A detailed understanding of the factors effecting degradation in performance over time is required, and is as such a major focus of development within the programme. Description of work: There are six main work packages within the project:%LWP1 Design and build of a MF-SOFC stack and system;%LWP2

In recent years, the general interest in routing for vehicular ad hoc networks (VANETs) has increased notably. Many proposals have been presented to improve the behavior of the routing decisions in these very changeable networks. In this paper, we propose a new routing protocol for VANETs that uses four different metrics. which are the distance to destination, the vehicles' density, the vehicles' trajectory and the available bandwidth, making use of the information retrieved by the sensors of the vehicle, in order to make forwarding decisions, minimizing packet losses and packet delay. Through simulation, we compare our proposal to other protocols, such as AODV (Ad hoc On-Demand Distance Vector), GPSR (Greedy Perimeter Stateless Routing), I-GPSR (Improvement GPSR) and to our previous proposal, GBSR-B (Greedy Buffer Stateless Routing Building-aware). Besides, we present a performance evaluation of the individual importance of each metric to make forwarding decisions. Experimental results show that our proposed forwarding decision outperforms existing solutions in terms of packet delivery.

In recent years, the general interest in routing for vehicular ad hoc networks (VANETs) has increased notably. Many proposals have been presented to improve the behavior of the routing decisions in these very changeable networks. In this paper, we propose a new routing protocol for VANETs that uses four different metrics. which are the distance to destination, the vehicles’ density, the vehicles’ trajectory and the available bandwidth, making use of the information retrieved by the sensors of the vehicle, in order to make forwarding decisions, minimizing packet losses and packet delay. Through simulation, we compare our proposal to other protocols, such as AODV (Ad hoc On-Demand Distance Vector), GPSR (Greedy Perimeter Stateless Routing), I-GPSR (Improvement GPSR) and to our previous proposal, GBSR-B (Greedy Buffer Stateless Routing Building-aware). Besides, we present a performance evaluation of the individual importance of each metric to make forwarding decisions. Experimental results show that our proposed forwarding decision outperforms existing solutions in terms of packet delivery.

This paper proposes an adaptation of the collision probability used in the measure of the available bandwidth designed
for Mobile Ad hoc Networks (MANETs) and which is described in ABE [12]. Instead, we propose a new ABE+ that
includes a new function to estimate the probability of losses. This new function has been specially designed for Vehicular
Ad hoc Networks, to be suited to the high mobility and variable density in vehicular environments. In this analysis we
do not only consider the packet size, but also other metrics, such as, density and speed of the nodes. We include the
ABE+ algorithm in the forwarding decisions of the GBSR-B protocol [14], which is an improvement of the well-known
GPSR protocol. Finally through simulations, we compare the performance of our new ABE+ compared to the original
ABE. These results show that ABE+ coupled with GBSR-B achieves a good trade-o in terms of packet losses and
packet end-to-end delay.

This paper proposes an adaptation of the collision probability used in the measure of the available bandwidth designed
for Mobile Ad hoc Networks (MANETs) and which is described in ABE [12]. Instead, we propose a new ABE+ that
includes a new function to estimate the probability of losses. This new function has been specially designed for Vehicular
Ad hoc Networks, to be suited to the high mobility and variable density in vehicular environments. In this analysis we
do not only consider the packet size, but also other metrics, such as, density and speed of the nodes. We include the
ABE+ algorithm in the forwarding decisions of the GBSR-B protocol [14], which is an improvement of the well-known
GPSR protocol. Finally through simulations, we compare the performance of our new ABE+ compared to the original
ABE. These results show that ABE+ coupled with GBSR-B achieves a good trade-o in terms of packet losses and
packet end-to-end delay.

Vehicular ad hoc networks (VANETs) have emerged to leverage the power of modern communication technologies, applied to both vehicles and infrastructure. Allowing drivers to report traffic accidents and violations through the VANET may lead to substantial improvements in road safety. However, being able to do so anonymously in order to avoid personal and professional repercussions will undoubtedly translate into user acceptance. The main goal of this work is to propose a new collaborative protocol for enforcing anonymity in multi-hop VANETs, closely inspired by the well-known Crowds protocol. In a nutshell, our anonymous-reporting protocol depends on a forwarding probability that determines whether the next forwarding step in message routing is random, for better anonymity, or in accordance with the routing protocol on which our approach builds, for better quality of service (QoS). Different from Crowds, our protocol is specifically conceived for multi-hop lossy wireless networks. Simulations for residential and downtown areas support and quantify the usefulness of our collaborative strategy for better anonymity, when users are willing to pay an eminently reasonable price in QoS.

Mobile ad hoc networks (MANETs) are infrastructureless
networks formed by wireless mobile devices. Recently,
the demand over multimedia services such as video streaming
has increased specially since the number of mobile end users is
growing as well. MPEG-2 VBR is one of the most fitting video
coding techniques for MANETs which improves the distribution
of video streams specially when it is used with a proper multipath
routing scheme. In this article, we aimed to design a routing
scheme to dynamically select the forwarding paths using a
game-theoretic approach over a multipath routing protocol. Our
proposal seeks to describe an equation of the probability p of
sending video frames through the best available path. p depends
on network parameters that vary throughout time. The aim is
that the most important video frames (I+P) will be sent through
the best path with a certain probability p and will be sent through
the second best path with a probability 1-p. To achieve that, we
carried out simulations done with fixed values of p and after that
we applied a lineal regression method to obtain the coefficients
of the equation for p. Simulations have been done to show the
benefits of our proposal where interfering traffic and mobility
of the nodes are present.

The constant mobility of people, the growing need to be always connected, the large number of vehicles that nowadays can be found in the roads and the advances in technology make Vehicular Ad hoc Networks (VANETs) be a major area of research. Vehicular Ad hoc Networks are a special type of wireless Mobile Ad hoc Networks (MANETs), which allow a group of mobile nodes configure a temporary network and maintain it without the need of a fixed infrastructure. A vehicular network presents some specific characteristics, as the very high speed of nodes. Due to this high speed the topology changes are frequent and the communication links may last only a few seconds. Smart cities are now a reality and have a direct relationship with vehicular networks. With the help of existing infrastructure such as traffic lights, we propose a scheme to update and analyse traffic density and a warning system to spread alert messages. With this, traffic lights assist vehicular networks to take proper decisions. This would ensure less congested streets. It would also be possible that the routing protocol forwards data packets to vehicles on streets with enough neighbours to increase the possibility of delivering the packets to destination. Sharing updated, reliable and real-time information, about traffic conditions, weather or security alerts, increases the need of algorithms for the dissemination of information that take into account the main beneffits and constraints of these networks. For all this, routing protocols for vehicular networks have the difficult task to select and establish transmission links to send the data packets from source to destination through multiple nodes using intermediate vehicles efficiently. The main objective of this thesis is to provide improvements in the communication framework for vehicular networks to improve decisions to select next hops in the moment to send information, in this way improving the exchange of information to provide suitable communication to minimize accidents, reduce congestion, optimize resources for emergencies, etc. Also, we include intelligence to vehicles at the moment to take routing decisions. Making them map-aware, being conscious of the presence of buildings and other obstacles in urban environments. Furthermore, our proposal considers the decision to store packets for a maximum time until finding other neighbouring nodes to forward the packets before discarding them. For this, we propose a protocol that considers multiple metrics that we call MMMR (A Multimetric, Map-Aware Routing Protocol ). MMMR is a protocol based on geographical knowledge of the environment and vehicle location. The metrics considered are the distance, the density of vehicles in transmission range, the available bandwidth and the future trajectory of the neighbouring nodes. This allows us to have a complete view of the vehicular scenario to anticipate the driver about possible changes that may occur. Thus, a node can select a node among all its neighbours, which is the best option to increase the likelihood of successful packet delivery, minimizing time and offering a level of quality and service. In the same way, being aware of the increase of information in wireless environments, we analyse the possibility of offering anonymity services. We include a mechanism of anonymity in routing protocols based on the Crowd algorithm, which uses the idea of hiding the original source of a packet. This allowed us to add some level of anonymity on VANET routing protocols. The analytical modeling of the available bandwidth between nodes in a VANET, the use of city infrastructure in a smart way, the forwarding selection in data routing byvehicles and the provision of anonymity in communications, are issues that have been addressed in this PhD thesis. In our research work we provide contributions to improve the communication framework for Vehicular Ad hoc Networks obtaining benefits toenhance the everyday of the population.

Road safety has become a main issue for governments and car manufacturers in the last twenty years. The
concept of Intelligent Transportation Systems (ITS) is used when talking about communication technologies between vehicles and
infrastructure to improve, among others, road safety. In this paper, we propose a warning service to prevent accidents by
alerting drivers about accidents and dangerous road conditions. This service includes the definition of a new broadcast dissemination mechanism. A VANET highway scenario is simulated to evaluate how the use of safety schemes decreases the driver’s reaction time when an unexpected situation occurs.

Wireless vehicular communications are a key technology to provide drivers with novel services such as collision avoidance, safety warnings and real-time traffic information. Other services are high-speed toll collection, infotainment and wireless ubiquitous connectivity. It is clear that vehicular communications will be a cornerstone of the future transport systems which will significantly change our daily lives. Vehicular ad hoc networks (VANETs) have rapidly emerged and raised novel research challenges such as the design of network protocols adapted to the specific features of VANETs, e.g. the high speed of vehicles. Also, the design of realistic simulation frameworks is an important goal to speed up the development of VANETs. This paper presents the design and evaluation of GBSR-B, a routing protocol based on GPSR that seeks to improve the performance of VANETs over urban scenarios. Our proposal includes a novel algorithm to select the optimal next-hop forwarding node. This paper also presents an alternative to the perimeter mode used in GPSR. We compare our proposal GBSR-B to GPSR and AODV using the network simulator NCTUns 6.0, showing better results in terms of packet losses.

Vehicular communication for intelligent transportation
systems will provide safety, comfort for passengers, and more
efficient travels. This type of network has the advantage to warn
drivers of any event occurred in the road ahead, such as traffic
jam, accidents or bad weather. This way, the number of traffic
accidents may decrease and many lives could be saved. Moreover,
a better selection of non-congested roads will help to reduce
pollution. Some other interesting services, such as downloading
of multimedia services, would be possible and available through
infrastructure along the roadside. Providing multimedia services
over VANETs may require a QoS-aware routing protocol that
often need to estimate available resources. In this paper, we
study the performance, in realistic VANET urban scenarios, of
an extension of AODV that includes the available bandwidth
estimator ABE [1]. AODV-ABE establishes forwarding paths
that satisfy the bandwidth required by the applications. The
results, obtained on the NCTUns simulator [2], show that AODVABE
could be used in urban-VANETs where vehicles’ speed is
moderate.

Road safety has become a main issue for governments and car manufacturers in the last twenty years. The development of new vehicular technologies has favoured companies, researchers and institutions to focus their efforts on improving road safety. During the last decades, the evolution of wireless technologies has allowed researchers to design communication systems where vehicles participate in the communication networks. Thus, new types of networks, such as Vehicular Ad Hoc Networks (VANETs), have been created to facilitate communication between vehicles themselves and between vehicles and infrastructure. New concepts where vehicular networks play an important role have appeared the last years, such as smart cities and living labs [1]. Smart cities include intelligent traffic management in which data from the TIC (Traffic Information Centre) infrastructures could be reachable at any point. To test the possibilities of these future cities, living labs (cities in which new designed systems can be tested in real conditions) have been created all over Europe. The goal of our framework is to transmit information about the traffic conditions to help the driver (or the vehicle itself) take adequate decisions. In this work, the development of a warning system composed of Intelligent Traffic Lights (ITLs) that provides information to drivers about traffic density and weather conditions in the streets of a city is proposed and evaluated through simulations.

Nowadays, video on demand is one of the services more highly appreciated and demanded by customers. As the number of users increases, the capacity of the system that provides these services must also be increased to guarantee the required quality of service. An approach to that end is to have available several videoservers at various distribution points in order to satisfy the different incoming demands (videoservercluster). When a movie demand arrives to such a cluster, a load balancing device must assign the request to a specific server according to a procedure that must be fast, easy to implement and scalable. In this article we consider the problem of appropriately splitting this load to improve on the system performance. After an analysis of the video packet generation, we point out the similarity between this problem and that of optimally routing packets in data networks. With this similarity in mind, a new mechanism to select the appropriate videoserver is proposed. The purpose of this mechanism is to minimize the average packet transfer time (waiting time plus transmission time) at the videoservercluster. In this way, we are able to obtain a dynamic load balancing policy that performs satisfactorily and that is very easy to implement in practice. The results of several experiments run with real data are shown and commented to substantiate our claims. A description of a practical implementation of the system is also included.

The number of portable electronic devices capable of maintaining wireless communications increases day by day. Such mobile nodes may easily self-configure to form a Mobile Ad Hoc Network (MANET) without the help of any established infrastructure. As the number of mobile devices grows, the demand of multimedia services such as video-streaming from these networks is foreseen to increase as well. This paper presents a proposal which seeks to improve the experience of the end users in such environment. The proposal is called dCW-MMDSR (dynamic Contention Window-Multipath Multimedia Dynamic Source Routing), a cross-layer multipath routing protocol which includes techniques to achieve a dynamic assignment of the Contention Window of the IEEE 802.11e MAC level.
In addition, it includes multipath routing suitable for layered coded video to improve the performance of the service. The operation is simple and suitable for low capacity wireless devices. Simulations show the benefits under different scenarios.

The number of portable devices capable of maintaining wireless communications has increased considerably in the last decade. Such mobile nodes may form a spontaneous self-configured network connected by wireless links to constitute a Mobile Ad Hoc Network (MANET). As the number of mobile end users grows the demand of multimedia services, such as video-streaming, in such networks is envisioned to increase as well. One of the most appropriate video coding technique for MANETs is layered MPEG-2 VBR, which used with a proper multipath routing scheme improves the distribution of video streams. In this article we introduce a proposal called g-MMDSR (game theoretic-Multipath Multimedia Dynamic Source Routing), a cross-layer multipath routing protocol which includes a game theoretic approach to achieve a dynamic selection of the forwarding paths. The proposal seeks to improve the own benefits of the users whilst using the common scarce resources efficiently. It takes into account the importance of the video frames in the decoding process, which outperforms the quality of the received video. Our scheme has proved to enhance the performance of the framework and the experience of the end users. Simulations have been carried out to show the benefits of our proposal under different situations where high interfering traffic and mobility of the nodes are present.

In the last years, wireless networks have become a widely spread type of communication technology and also a challenging scientific area for new fields of research. Many contributions in ad hoc networks, such as WSNs (Wireless Sensor Networks) and VANETs (Vehicular Ad Hoc Networks), have been proposed. Nowadays, the huge amount of cars in transit has raised a big interest in vehicular communication technologies. A new type of network has been developed, named HSVN (Hybrid Sensor and Vehicular Network) in which WSNs and VANETs cooperate with the aim of improving road safety. Recent projects, such as CVIS [1] and COMeSafety [2], are focused on improving the road driving. This type of approaches will warn the driver and the co-pilot of any event occurred in the road ahead, such as traffic jam, accidents, bad weather, etc. This way, the number of traffic accidents may decrease and many lives might be saved. Besides, a better selection of non-congested roads will help to reduce pollution.
In addition, other attractive services, such as downloading of multimedia services or Internet browsing, would be easily available through infrastructure along the roadside.
Transportation in motorways will be easier, safer and more comfortable for passengers. In this paper a HSVN platform is presented, also a communications protocol between VANETs and WSNs is described and evaluated using the NCTUns [3]
simulator.

The increasing spread of mobile nodes along with the technical advances
in multi-hop MANETs (Mobile Ad hoc NETworks) make this
kind of networks an important type of access network of next generation.
The demand of multimedia services from these networks is expected
to significantly grow in the next years. Multimedia services, though, require
the provision of Quality of Service (QoS). Nevertheless, the highly
dynamic nature of MANETs, the energy constraints, the lack on centralized
infrastructure and the variable link capacity, makes the QoS provision
over MANETs a matter that challenges attention. These features make self-configuration and system adaptation questions of major importance when developing a QoS-aware framework. To tackle this issue, we have designed a-MMDSR (adaptive-Multipath Multimedia Dynamic Source Routing), a multipath routing protocol able to self-configure dynamically
depending on the state of the network. The approach includes cross-layer techniques especially designed to improve the end-to-end performance
of video-streaming services over IEEE 802.11e Ad Hoc networks.
Besides, a straightforward analytical model to estimate the path error probability is presented. This model is used by the routing scheme to estimate the lifetime of the paths. In this way, proper proactive decisions can be made before the paths get broken. The model simplicity is appropriate for low capacity wireless devices. Simulation results validate the proposal and show the improvement on standard DSR (Dynamic Source Routing) and on a previous static version.

Mobile ad hoc networks (MANETs) are infrastructureless networks formed by wireless
mobile devices with limited battery life. In MANETs for civilian applications, the network
nodes may not belong to a single authority and they may not have a common goal. These
MANETs are particularly vulnerable to selfish behavior, as some nodes may prefer saving
resources to forward data. There are a few generic reputation-based systems for MANETs
which could be used to enforce cooperation among nodes. However, we envision that
the system performance can be highly improved by using cross-layer techniques that take
into account the specific characteristics of each particular service. In this article, we propose
a distributed and easy-to-implement routing mechanism based on reputation for
the provision of MPEG-2 video-streaming services over MANETs. The main novelty that
we introduce regarding the existent literature is that our proposal is service aware, that
is to say, we consider the video-streaming service characteristics to develop a cross-layer
design with the routing protocol. In addition, we do not introduce extra signaling overhead
to monitor reputation because we use the standard video-streaming end-to-end signaling.
Finally, simulation results show that our proposal clearly outperforms both standard
Dynamic Source Routing (DSR) and OCEAN (a generic reputation-based mechanism).